The video assistant referee (VAR) system, which is being deployed in Russia for the first time in World Cup history, featured in three key moments during Monday's dramatic clash between Portugal and Iran.
Referee Enrique Caceres stopped the game three times for VAR reviews, awarding one penalty to each side. Although the VAR system got the first decision correct when the referee awarded Portugal a penalty after Ronaldo was fouled in the box, Iran's VAR-assisted injury-time spot kick seemed a harsh decision to some.
READ MORE: Portugal Held to 1-1 Draw by Iran at World Cup Match in Saransk
Another controversial episode took place when Cristiano Ronaldo elbowed Morteza Pouraliganji. While Iran's players called on the referee to send off Portugal's superstar, Ronaldo got away with just a yellow after Enrique Caceres consulted a pitchside monitor.
Some users believe Ronaldo didn't even deserve a yellow.
This opinion, however, doesn't seem somewhat unanimous.
Others argued that Ronaldo's side deserved a more severe punishment.
In another Group B game between Spain and Morocco, Gerard Pique escaped a red card for his two-footed challenge on Morocco's Boutaib.
Some embarrassed fans took to Twitter to slam what they called a "disgrace."